feat(explore): support show annotation label [ID-8] (#17307)

* feat(explore): support always show annotation label

* fix: lint

* fix: lint

* Hopefully appeasing the linter

* fix: lint

* Update superset-frontend/src/explore/components/controls/AnnotationLayerControl/AnnotationLayer.jsx

Co-authored-by: Geido <60598000+geido@users.noreply.github.com>

* change to allow none

* lint

Co-authored-by: Evan Rusackas <evan@preset.io>
Co-authored-by: Geido <60598000+geido@users.noreply.github.com>

docs/src/resources/openapi.json

@@ -154,6 +154,10 @@
             "description": "Should the layer be shown",
             "type": "boolean"
           },
+          "showLabel": {
+            "description": "Should the label always be shown",
+            "type": "boolean"
+          },
           "showMarkers": {
             "description": "Should markers be shown. Only applies to line annotations.",
             "type": "boolean"
@@ -201,6 +205,7 @@
         "required": [
           "name",
           "show",
+          "showLabel",
           "showMarkers",
           "value"
         ],